Silver wattle
Acacia dealbata. Family Fabaceae. Tree.
Also called Mimosa, Blue wattle.
Silver wattle is a fast-growing evergreen tree from southeastern Australia, grown for its finely divided silver-grey foliage and fragrant yellow flowers in late winter and early spring. It needs a mild climate and room to develop; its suckering roots and invasive behaviour make it unsuitable for some regions.
At a glance
- Sun
- Full sun, sheltered from strong winds and cold, drying winter winds.
- Water
- Water regularly while establishing. Established trees tolerate dry periods, but young trees and container plants need watering during prolonged drought.
- Soil
- Well-drained, acidic to neutral soil; sandy or loamy soils suit it well. Avoid waterlogged ground and strongly alkaline soil, which can cause yellowing.
- Height
- 30-60 ft (9-18 m), sometimes taller in favourable conditions
- Spread
- 20-40 ft (6-12 m)
- Flowers
- Late winter to early spring; fragrant, bright yellow flower balls carried in branching clusters.
- Foliage
- Evergreen, finely divided, fern-like leaves with numerous tiny silver-grey to blue-grey leaflets.
- Growth
- Fast
- Care needed
- Medium
The year at a glance
- Pollinators
- Drought tolerant
- Heat tolerant
- Wildlife
- Fragrant
| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Flowers | ||||||||||||
| Plant |
Northern hemisphere months. In Australia, shift them by six.
- Difficulty
- Hard
- Toughness
- Needs looking after
Will it suit your garden?
Pick your zone, country, light and whether you have pets.
Full sun is 6 or more hours of direct sun a day, part shade 3 to 6 hours, shade under 3.
How it grows
Planting day
7 ft (2 m)
After 1 year
9 ft (2.9 m)
After 2 years
12 ft (3.8 m)
After 3 years
15 ft (4.7 m)
After 5 years
21 ft (6.4 m)
About 13 years to full size.
From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.
Good to know
- Cats and dogs
- Safe
- Native to
- Australia
- Invasive in
- the US
- In the garden
- Spreads vigorously: plan to contain it.
- Growth rate
- Fast
Care
Jobs through the year
- WaterApr–May, Sep–Oct, every 14 days
- Deep-water established trees only if dry; young trees need more frequent watering for two years.
- WaterJun–Aug, every 14 days
- Water established trees deeply during prolonged drought; check young plants and pots more often.
- WaterJan–Mar, Nov–Dec, every 21 days
- For frost-free overwintered pots, water sparingly when the surface dries; never leave saturated.
- MulchApr–May
- Apply 5–8 cm of organic mulch, keeping it clear of the trunk.
- PruneApr–May
- After flowering, lightly shape and remove damaged or crossing branches; avoid old-wood cuts.
- PruneMay–Oct, every 30 days
- Remove unwanted suckers and seedlings promptly.
- ProtectApr–May
- Check invasive-plant restrictions before planting; choose a sunny, sheltered position.
- ProtectJan–Apr, Oct–Dec
- Not reliably hardy in zones 6–7; overwinter in a bright, frost-free container space.
- Check local invasive-plant restrictions before buying or planting.
- Plant after the main frost risk has passed, in a sunny, sheltered position away from paving and drains.
- Water deeply through the first two growing seasons, allowing the surface soil to dry between waterings.
- Apply a 2-3 in (5-8 cm) organic mulch, keeping it clear of the trunk; routine feeding is usually unnecessary.
- Stake young trees only if needed, using flexible ties, and remove the support once the roots hold the tree firmly.
- Remove unwanted suckers and seedlings promptly; protect young trees from frost with horticultural fleece.
Pruning. Prune lightly just after flowering, removing dead, damaged or crossing branches and shaping young trees. Avoid hard cuts into old wood and repeated topping, which can leave a poor framework and encourage unwanted shoots.
Through the year
- Late winter
- Enjoy the flowers and protect young plants if frost is forecast.
- Spring
- Plant once severe frost is unlikely; water thoroughly and mulch.
- Spring
- After flowering, remove damaged branches and lightly shape young trees.
- Summer
- Water establishing trees during dry spells and check for scale insects.
- Autumn
- Pull seedlings, remove unwanted suckers and check that tree ties are not tight.
- Winter
- Check for wind damage and keep container plants in a bright, frost-protected position where winters are cold.
In the garden
- Use as a specimen in a spacious, mild-climate garden where its spreading crown can develop freely.
- Place behind low, sun-loving shrubs so its silver foliage provides a contrasting backdrop.
- Combine with rosemary, lavender and rockroses in a well-drained Mediterranean-style planting where it is not invasive.
- Use in Australian native gardens within its natural region for early flowers and evergreen structure.
Garden styles it suits: Australian native, Mediterranean, Winter interest, Sensory garden, Woodland and Wildlife garden.
Plant it with: Rosemary, Lavender, Rockrose, Westringia and Kangaroo paw.
Wildlife: Flowers provide pollen for bees and other insects. The canopy offers shelter and nesting cover, but outside its native range dense stands can displace more valuable local habitat.
Problems to watch for
- Frost damage: young shoots and flower buds can be killed by cold; choose a sheltered site, protect young trees and wait until spring growth begins before removing damaged wood.
- Yellow leaves on alkaline soil: iron becomes less available; use a suitable chelated iron treatment for temporary relief, but choose another tree if the soil is strongly alkaline.
- Root rot in wet ground: improve drainage before planting and avoid frequent watering once established; badly affected trees may not recover.
- Scale insects: inspect stems and leaf stalks, encourage natural predators and treat reachable infestations with a locally approved horticultural oil according to its label.
Safety
It is not generally known as a common poisoning plant for people, cats or dogs, but reliable species-specific safety information is limited, especially for horses. Do not use its seeds, pods, bark or foliage as food or allow livestock to browse it; the seriousness of ingestion cannot be confidently stated.
Where it spreads. Spreads by seed and root suckers. It is invasive in parts of coastal California, Portugal, Spain, southern France, Italy, South Africa, Chile and New Zealand, and is an environmental weed in parts of Australia outside its native range, including southwestern Western Australia. Restrictions vary locally; cutting a tree down may trigger vigorous suckering.
Easily confused with
Cootamundra wattle (Acacia baileyana)
Usually a smaller tree with shorter, more compact leaves and far fewer pairs of primary leaf divisions; silver wattle has longer, more finely divided leaves.
Black wattle (Acacia mearnsii)
Has greener foliage and pale cream to pale yellow flowers, usually later in the season; silver wattle has silvery foliage and brighter yellow flowers.
Silk tree (Albizia julibrissin)
Has similar fern-like leaves but is deciduous and produces pink, silky flowers in summer rather than yellow flower balls in late winter or spring.
The name
The Latin epithet dealbata means whitened, referring to the pale coating on its young growth and foliage, which also gives rise to the name silver wattle.
Propagation. Usually grown from seed. Pour hot water over the seeds, leave them to soak as the water cools for about 24 hours, then sow swollen seeds in a free-draining seed mix in spring. Seed-grown plants vary; avoid propagating it where it is invasive.
Checked against open data
- Accepted botanical name
- Acacia dealbata
- In the US and Canada
- Introduced in the lower 48 states.
- Native range
- New South Wales, Tasmania and Victoria.
- Measured
- Average height 970 cm.
Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.
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